GROUND WATER ATLAS of the UNITED STATES
Connecticut, Maine, Massachusetts, New Hampshire, New York, Rhode Island,
Vermont
HA 730-M

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SANDSTONE AQUIFERS

INTRODUCTION

Sedimentary rocks that consist primarily of sandstone form aquifers in
several areas of New York, Massachusetts, and Connecticut (fig.
102). The Potsdam Sandstone of Cambrian age in parts of northern New
York together with the overlying Theresa Formation, also of Cambrian age,
is an aquifer that yields small to moderate quantities of water to wells.
Small quantities of water also are obtained from sandstones of the Silurian
Medina Group in the Mohawk River Valley and along the south shore of Lake
Ontario. In the Connecticut River Valley of Connecticut and Massachusetts,
sandstones in the Newark Supergroup of early Mesozoic age form a significant
aquifer. These rocks also are present in an early Mesozoic basin in New
Jersey that extends into southeastern New York. Although sandstone aquifers
generally are limited in areal extent and yield small to moderate quantities
of water, they are significant sources of water for rural, domestic, industrial,
and small-community supplies in their area of occurrence where the surficial
aquifer system is not present.

GEOLOGY

The Cambrian Potsdam Sandstone forms a discontinuous fringe around the
northern and western borders of the Adirondack Mountains in New York. The
Potsdam generally consists of tan to grayish-white quartz sandstone with
siliceous and cal-careous cement. Locally, some of the basal sandstone beds
are either red from hematitic cementation or green from chloritic cementation.
Basal beds of coarse conglomerate are present in some places.

The Potsdam Sandstone overlies granite and hornblende-syenite gneiss
of Precambrian age (fig. 103); its thickness
ranges from a featheredge to about 200 feet. The Potsdam might have formed
originally as a beach deposit. It grades upward into the Theresa Formation
of marine origin, which consists of hard, bluish-gray, thinly bedded, sandy
dolomite with calcareous sandstone layers in the basal part. The upper beds
of the Theresa Formation range from calcareous and dolomitic sandstones
to sandy dolomite, which is characterized by numerous fossils. The thickness
of the Theresa Formation ranges from a featheredge to about 70 feet. Dolomite
and limestone of the Black River Group of Ordovician age overlie Cambrian
rocks.

The sedimentary rocks of central Connecticut and Massachusetts have been
assigned to the Newark Supergroup of early Mesozoic age (fig.
102). They are lithologically similar to the Newark Supergroup, which
consists of red sandstone, shale, and conglomerate and fills a number of
fault-block basins that extend from New Jersey to South Carolina. These
basins are discussed in Chapter L of this Atlas. In Connecticut and Massachusetts,
these sedimentary rocks uncon-formably overlie pre-Mesozoic igneous and
metamorphic rocks in the lowland trough of the Connecticut River Valley.
The sedimentary rocks are bounded on the east by a major fault with several
thousand feet of vertical displacement (fig. 104).
The fault formed an eastward-tilting trough that became filled with sandstone
and interbedded lava flows, which are in contact with pre-Mesozoic crystalline
rocks beneath and across the fault. The rocks in the trough dip eastward
at about 15 degrees. They feather out to the west to expose the underlying
pre-Mesozoic bedrock. Glacial deposits overlie the early Mesozoic rocks.

The Newark Supergroup consists of continental deposits of reddish arkosic
sandstone (fig. 105), feldspathic sandstone,
conglomerate, and shale, with some limestone and siltstone. The sandstone
is interbedded with at least three thick basaltic lava flows (fig.
106) that also dip eastward at about 15 degrees. Because they are hard
and resistant to erosion, the lava flows typically form topographic ridges.
The softer sandstone, which is easily eroded, typically forms lowlands and
rarely crops out.

The Newark Supergroup has been subdivided into three formations: the
New Haven Arkose, the Meriden Formation, and the Portland Arkose. The New
Haven Arkose is the lowermost formation and consists of all sedimentary
rocks below the lowermost lava flow. The Meriden Formation consists of the
three lava flows and interbedded sandstone. The Portland Arkose is the uppermost
formation and includes all sedimentary rocks above the uppermost lava flow.
Maximum thickness of the Meriden Formation is about 800 feet. The maximum
thickness of the Newark Supergroup is estimated to be about 4,000 feet.

GROUND-WATER HYDROLOGY

The sandstone aquifer in northern New York (fig.
102) generally is hydraulically connected with the aquifer in overlying
carbonate rocks and, for the most part, the two aquifers are confined by
overlying glacial deposits. Hydraulic heads in the glacial deposits generally
are from 30 to 40 feet higher than the potentiometric surface of the two
aquifers; therefore, recharge to the sandstone aquifer is by downward percolation
of water through the overlying glacial deposits and carbonate rocks. Where
the sandstone aquifer is overlain by glacial deposits, recharge to the aquifer
is by downward percolation of water through the overlying deposits. After
the water enters the sandstone aquifer, it moves horizontally from recharge
areas in the interstream highlands toward the streams and Lake Ontario.
At these surface-water bodies, the water moves upward through the carbonate
rocks or the glacial deposits or both into the surface-water bodies.

The intergranular porosity of the sandstone aquifer generally ranges
from about 4 to 30 percent with an average of only about 10 percent because
most of the intergranular space is filled with siliceous or calcareous cement.
Therefore, ground-water movement in the aquifer is primarily through second-
ary openings, such as joints, fractures, and bedding-plane openings. Data
for 12 domestic wells completed in the sandstone aquifer in northern New
York indicate that the wells penetrated from 16 to 55 feet of sandstone
(average 32.5 feet) and yielded from 3 to about 30 gallons per minute. Wells
with the largest yields were completed only in the Theresa Formation, thus
indicating that it might be more fractured than the Potsdam Sandstone.

The sandstone of the Newark Supergroup also is well cemented by carbonate
cement that has filled many of the intergranular openings; porosity is estimated
to be about 7 percent. Thus, water in the aquifer in the lower Mesozoic
sandstone primarily is contained in and moves through secondary openings,
such as joints, fractures, and bedding planes. Bedding-plane openings probably
transfer the greatest quantity of water.

Yields from 688 wells completed in the sandstone aquifer of the Newark
Supergroup ranged from 0.5 to 578 gallons per minute; the average yield
was 34 gallons per minute. The depths of these wells range from 40 to 973
feet with an average depth of 203 feet.

Yields from the interbedded basaltic lava flows, which have only fracture
permeability, generally are smaller than those from the sandstone aquifer.
The average yield of 53 wells completed in the basalt ranged from 1.5 to
about 50 gallons per minute with an average yield of 13 gallons per minute.
The depths of these wells range from 60 to 500 feet.

Yields to wells completed in either the sandstone aquifer or the basalt
tend to be larger in areas where these aquifers are overlain by the surficial
aquifer system rather than in areas where they are overlain by till. This
indicates that the surficial aquifer system provides storage for water that
subsequently moves downward into the aquifers as water is withdrawn from
them.

Ground-water movement through the sandstone aquifer of the Newark Supergroup
is not well defined; however, the presence of freshwater at depths of several
hundred feet in the aquifer indicates that regional ground-water movement
occurs. Recharge occurs in areas where the aquifer crops out and in upland
areas where the sandstone aquifer is overlain by permeable sand and gravel
of the surficial aquifer system. Water in the sandstone aquifer mostly moves
down a slight hydraulic gradient in local flow systems to areas of discharge
at small streams where it moves upward to the stream through the surficial
aquifer system and becomes part of the streamflow.

There also is a regional flow system in which the water moves deeply
into the aquifer and toward the Connecticut River where the water is discharged
through the surficial aquifer system to the river. Some water also discharges
directly to the ocean in the coastal areas of the Connecticut River Basin.

Few wells penetrate more than about 500 feet into the sandstone aquifer,
and little hydrologic information is available beyond that depth. Because
the number of joints, fractures, and bedding-plane openings in all types
of rock typically decrease with depth, permeability of the sandstone aquifer
should similarly decrease until ground-water movement ceases at some depth.
Decreased circulation of ground water results in an increase of dissolved
minerals in the water. Thus, the boundary of freshwater is lower in the
sandstone aquifer, probably within about 1,000 feet of the land surface,
below which use of the aquifer is limited by a decrease in permeability
and by a deterioration in water quality.

GROUND-WATER QUALITY

The chemical quality of water in sandstone aquifers of the Newark Supergroup
and in Lower Paleozoic rocks generally is suitable for drinking, as well
as most other uses. A summary of water-quality data for water from the aquifers
in the Newark Supergroup in Connecticut and southeastern New York and from
the Potsdam Sandstone and sandstone of the Medina Group in north-central
New York is shown in table 14. Median, maximum, and minimum values of each
chemical constituent for about 100 chemical analyses are listed.

Median values of calcium, sulfate, hardness, and dissolved solids shown
in table 14 indicate that excessive concen-trations of dissolved minerals
generally are not a problem. Locally, large maximum values indicate that
highly mineralized water exists, particularly at depth in the sandstone
aquifers of the Newark Supergroup and in sandstone of the Medina Group.
Large sulfate concentrations may result from dissolution of gypsum that
is disseminated in places in the sandstone of the Newark Supergroup. The
calcium from the gypsum contributes to excessive hardness and large concentrations
of calcium. Both ions contribute to increased concentrations of dissolved
solids.

Large chloride concentrations in water from aquifers in the Newark Supergroup
of Rockland County, N.Y. (table 14), may indicate
local contamination from road-deicing chemicals or some other source of
chloride on the land surface. Locally, large chloride and calcium concentrations
in water from sandstone of the Medina Group in Wayne County, N.Y., contribute
to dissolved-solids concentrations in excess of 8,000 milligrams per liter.
In general, water from sandstone of the Medina Group appears to be more
mineralized than that in the sandstone aquifers in the Newark Supergroup.

FRESH GROUND-WATER WITHDRAWALS

Aquifers in the Cambrian sandstone of New York and the lower Mesozoic
sandstone of Connecticut and Massachusetts generally yield only small quantities
of water to wells. Therefore, they are used primarily as a source of supply
for households, commercial establishments, and small communities and industries
that require only modest quantities of water. About 28 percent, or 29 million
gallons per day, of the total water withdrawn from the sandstone aquifers
in Segment 12 during 1985 was withdrawn for domestic and commercial use
(table 15). In Connecticut and Massachusetts,
74 percent (fig. 107), or about 16 million gallons
per day, of the water withdrawn from these aquifers was used for domestic
and commercial purposes.

Water from sandstone aquifers also is used for industrial and mining
purposes, especially in New York. Withdrawals for these use categories accounted
for about 38 percent, or about 40 million gallons per day, of total withdrawals
from the sandstone aquifers in the three States during 1985 but accounted
for about 46 percent, or about 39 million gallons per day, of the total
water withdrawn in New York. Water was withdrawn for industrial and mining
uses, primarily for inplant domestic uses, gravel pit or quarry dewatering,
boiler makeup water, and gravel washing rather than for use as industrial
process water.

Agricultural use accounted for only about 1 percent, or about 1.3 million
gallons per day, of total withdrawals from the sandstone aquifers during
1985. This water was used largely for stock watering and milk processing.

In New York and Connecticut, about 33 percent, or about 35 million gallons
per day, of the total water withdrawn from the sandstone aquifers was used
for public supply (table 15). This use, however,
generally was in small communities or as a supplemental supply to surface
water in larger communities because of the generally limited yields of wells
completed in the sandstone aquifers.

Total withdrawals from the sandstone aquifers in the three States were
about 106 million gallons per day during 1985 (fig.
107). The largest withdrawals, which were about 85 million gallons per
day, were in New York. Connecticut and Massachusetts withdrew about 21 million
gallons per day.